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Author Topic: RPM's  (Read 1478 times)

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Offline Lnewman

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RPM's
« on: December 27, 2013, 05:12:59 pm »
To better adjust the carboretors on my saws (Stihl 170, 210, MS290, and MS441 and oldHomelite Super XL) I recently purchased a tachometer.   But I'm confused on the optimal RPM's for the low and high.

The manuals say 2800 idle speed so is that the best low adjustment for all saws?

There is a 8500 to 9500 RPM figure in the manuals that says "engine power to ISO 7293 --- whatever that means!  So would that be the best high adjustment.
Or would the 13,000 RPMs that is the "maximum permissible speed with bar and chain" be the better setting?

Greatly appreciate any knowledgable guidance.
Stihl 170, 210MS, 290MS, 441MS and Hudson bandsaw

Offline beenthere

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Re: RPM's
« Reply #1 on: December 27, 2013, 06:59:57 pm »
From what I recall reading on this Forum, tuning was done better by ear for each saw rather than to an RPM.

Maybe you have read that too, and got a different interpretation of what was said.
A lot of chainsaw experts on the Forum to help you get to the right answer... or several right answers.  ;D
south central Wisconsin
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Offline HolmenTree

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Re: RPM's
« Reply #2 on: December 27, 2013, 07:51:16 pm »
Different specs for different saw companies. Some companies spec their saws r.p.m. while cutting in the wood, others WOT with no load.

Offline ZeroJunk

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Re: RPM's
« Reply #3 on: December 27, 2013, 09:46:38 pm »
 I don't trust my ear well enough to get a saw as lean as it was probably meant to be run. I will be richer than tuned with a tach. I don't know that there is much downside to being a little rich, but there is to being a little too lean.

I wouldn't worry about the idle RPM as long as the chain isn't spinning. I usually tune up until the chain starts spinning and then back off until it stops.

I don't know a good way to tune RPM while cutting in the wood since you can make it whatever depending on how much pressure you put on the saw. If you can time your cuts and tune to the fastest cutting time, that will work.

Offline sawguy21

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Re: RPM's
« Reply #4 on: December 27, 2013, 10:08:04 pm »
Richen it until it sounds sick then gradually lean out no load
 until it starts to flutter. It will smooth out in the cut.
old age and treachery will always overcome youth and enthusiasm

Offline Lnewman

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Re: RPM's
« Reply #5 on: December 28, 2013, 08:44:37 am »
Does anyone know what "engine power to ISO 7293 "   means?
Stihl 170, 210MS, 290MS, 441MS and Hudson bandsaw

Offline dgdrls

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Re: RPM's
« Reply #6 on: December 28, 2013, 09:10:20 am »
http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=25973

719940
ISO 7293:1997
Forestry machinery - Portable chain saws - Engine performance and fuel consumption

standard published 12/01/1997 by International Organization for Standardization

this is what I was able to find.   
check the web for general tuning procedures.

Newer saws are so fast you need the tach'  to set to spec full rpm,
low speed should clean idle without the chain moving with the brake off .

DGDrls

Offline NCFarmboy

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Re: RPM's
« Reply #7 on: December 28, 2013, 09:12:32 am »
I'm not a Stihl man but Husky for ex lists a spec of 9600rpm and a max rpm of 13,500 w/bar and chain no load.  If you tune to 13,500 put under load rpm's drop to approx 9,600.  I assume that is what ISO 7593 is referring to (9600 rpm's).  Hopes this helps.  I personally use max rpm's on my customers saws.  If max rpm is 13,500 I usually set around 13,200 a little rich.
Shep
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Offline JohnG28

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Re: RPM's
« Reply #8 on: December 28, 2013, 09:19:14 am »
The number you are referring to, 9600 rpm in this case, should be the max power output of the saw.
Stihl MS361, 460 & 200T, Jonsered 490, Jonsereds 90, Husky 350 & 142, Homelite XL and Super XL

Offline John Mc

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Re: RPM's
« Reply #9 on: December 28, 2013, 11:01:15 am »
The number you are referring to, 9600 rpm in this case, should be the max power output of the saw.

And that is generally what you are aiming for in the cut.
Small time fire-wooder in a neighborhood cooperative.

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Offline Jiles

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Re: RPM's
« Reply #10 on: December 28, 2013, 12:09:48 pm »
I have 12 chainsaws. I do not use an RPM tack. because I don't consider any of them to be accurate except the ridiculously priced ones.
I never hold a chainsaw wide open for more then enough time to just reach max RPM. When I find that RPM, I slightly richen the mixture--about 1/8-1/4 turn, and then check in the cut.
With any two cycle engine, it is critical that you have the correct wide open adjustment that looses RPM but runs cleanly during the cut. When lifting the saw out of cut, you should witness a "fluttering-4 cycling sound.
You will probably notice that the saw will run different on different octane fuels and that has to be addressed.
Its just that sensitive!
Satisfy needs before desires

Offline Fatcougar

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Re: RPM's
« Reply #11 on: December 28, 2013, 12:21:38 pm »
Good Morning All.
 Lnewman, you might want to have a look at the Madsens site. They have some very good information on their page about chainsaw tuning with wav files so you can hear what it should sound like. There is also a lot of good information on oil mix, fuel and that kind of thing... very informative. My much better half bought me a EDT7 tach for Christmas so I thought it would be a great time to do a muffler mod on my old 026. Once I had opened up the muffler hole to around 75% percent of the exhaust port size , I turned out the L and H screws about a half turn to be on the safe side, then ran it and tried to tune by ear just to see how close I could get . I didn't do too bad but ended up only at about 11,500 at wide open throttle. I used the tach to finish the adjustments at around 13, 200 and just left it there. I was very surprised at how much more power the saw seemed to make in the cut with a simple muffler mod. I think my saw has always been running a bit too rich from what I am seeing from this experiment.
      In any case , thanks very much for all the great information from the members of this site... made doing a simple muffler mod a lot of fun and with a good result...... starting to ramble, sorry. Go check out Madsens!  :)
Fatcougar
Stihl 461-R
Stihl 026
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Offline Lnewman

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Re: RPM's
« Reply #12 on: December 29, 2013, 03:57:49 pm »
Seems like the consensus is to set the hi RPMs just a little lower than the maximum RPMs specified in the manual unless you have a highly trained ear and can set it that way.   Does anyone have any problems with that solution?
Stihl 170, 210MS, 290MS, 441MS and Hudson bandsaw

Offline CTYank

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Re: RPM's
« Reply #13 on: December 31, 2013, 02:06:24 am »
IME, forget the tach. I've seen two dealer "experts" use that method; the saw now runs great since I ran the H needle IN about 3/4 turn.

(All adjustments should be made with warm engine.)

The trick is to set the H needle so the engine 2-strokes cleanly @WOT in the cut AND starts to 4-stroke when you lift the bar slightly. You might, or might not, want to check what the tach tells you then, if only for giggles. That's as good as it gets. If it doesn't 4- stroke, go richer in small steps.

That's essentially what "auto-tune" does- periodically makes minor H adjustments and retains them if rpm under load goes up, else back-tracks. (Don't pin me down onp tails.) Focus on rpm under load, not while screaming with no load.
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Offline ZeroJunk

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Re: RPM's
« Reply #14 on: December 31, 2013, 09:38:31 am »
IME, forget the tach. I've seen two dealer "experts" use that method; the saw now runs great since I ran the H needle IN about 3/4 turn.

(All adjustments should be made with warm engine.)

The trick is to set the H needle so the engine 2-strokes cleanly @WOT in the cut AND starts to 4-stroke when you lift the bar slightly. You might, or might not, want to check what the tach tells you then, if only for giggles. That's as good as it gets. If it doesn't 4- stroke, go richer in small steps.

That's essentially what "auto-tune" does- periodically makes minor H adjustments and retains them if rpm under load goes up, else back-tracks. (Don't pin me down onp tails.) Focus on rpm under load, not while screaming with no load.


The target no load RPM on that saw is 13000. If you turned it 3/4 turn past that good luck in the contest.

Offline ladylake

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Re: RPM's
« Reply #15 on: December 31, 2013, 10:19:55 am »

Sound to me like CT has it set right no matter how it was set by the dealer.  I've gotten saws in straight from dealers set from pig rich to burn up lean, no tach here either.   Steve
Timberking B20 9000 hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Dino setter

Offline ZeroJunk

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Re: RPM's
« Reply #16 on: December 31, 2013, 11:01:17 am »
Just because you run in to somebody who does not understand how to use a tach doesn't mean they are not the most accurate way to tune.

I'm sure that you guys know how to tune a saw, but trying to explain what you are hearing to somebody new to saws over the internet is impossible. Letting the saw get to operating temperature and tuning it a few hundred RPM below max WOT to allow for differences in fuel is pretty simple. And accurate.

If I am going to buy a saw I would much rather have it done that way than from somebody I don't know who tuned it by ear.

And, if it blows turning rated RPM I don't know what you think was going to happen anyway.

Offline JohnG28

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Re: RPM's
« Reply #17 on: December 31, 2013, 11:31:41 am »
http://www.madsens1.com/mnu_sawmaint.htm

Go here. There are audio files in the tuning section to give you an idea what rich lean and in between sounds like. Makes things make much more sense.
Stihl MS361, 460 & 200T, Jonsered 490, Jonsereds 90, Husky 350 & 142, Homelite XL and Super XL

Offline Fatcougar

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Re: RPM's
« Reply #18 on: December 31, 2013, 11:35:59 am »
I understand what CT is getting at... there are unfortunately a small percentage of service (Admin edit) out there who do not take the time to do a good job for the customer. The problem I experienced personally with setting the H screw by ear was that it would 4 stroke and then 2 stroke immediately when you put some load on it like he says, but in my case it would do that over about a 2000 rpm range. I personally don't have the experience to know where in that range is the proper setting. The thought that I might be running too lean or not getting the power I should be by being rich is something that is very important to me in light of what kind of money a new chainsaw costs.
So for me I definately check with the Tach just for piece of mind. Great points by both sides on this discussion.
Fatcougar
Stihl 461-R
Stihl 026
New Holland TC30
Rankin 3 point Splitter

Offline Huskstihl

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Re: RPM's
« Reply #19 on: December 31, 2013, 11:43:27 am »
When I tune by ear I always wind up at least 1000 rpm short of "maximum".  Starting to 4 stroke when you ease up at all will lead to a very rich tune.  There's nothing wrong with that, and nobody ever hurt a saw that way, but they make more power and maintain a higher chain speed when tuned closer to spec.  My ported saws all have unlimited coils.  The limited coils can confuse both the ear and the tach as the rpm's "bounce" against the limiter.  When I am tuning a limited saw with a tach I start very rich and slowly move towards the limit.  If I get too close the tach goes crazy.  Unlimited coils are much easier with the tach. In that territory though, you kinda have to take the word of the builder as how far you can go safely with the saw.
I also do not want my saw lugging 9500rpm's in the cut.  It may be where the saw makes the most power, but saws don't have transmissions, and the higher rpm you can run in the cut, the faster stuff gets done.  If I had an 084 with a 50" it would be different



This is tuned with a tach to 13,400 with an 8 pin.  You can hear it 4-stroking out of the cut as well